A known road planer refers to a self propelled milling machine, generally used for removing a portion of asphalt road pavement in order to restore the road with re-deposition of renovated road-surface (repaving).
In the present invention the definitions “road planer” and “milling machine” are considered equivalent.
The road planer or milling machine consists of a self propelled chassis, supported by crawler tracks, or wheels, generally equipped with hydraulic actuators, powered by a diesel engine and having a milling drum to mill the asphalt road surface for repaving.
A milling drum is supported by the chassis transversally to the direction of travel, being directly operated by the diesel engine through a mechanical transmission, or by a hydraulic transmission.
Said crawler tracks or wheels are connected to telescopic columns, which consent the chassis to achieve the correct height and attitude to get the requested milling profile.
The material, milled by the drum, is removed by one or more conveyor belts, and finally discharged at the front section of the machine, or at its rear section. In the first case the milled material is discharged into a transport vehicle, which precedes the milling machine, whilst in the second case the vehicle follows the milling machine, running backward.
During the milling operation dusts arise, caused by the partial crushing of the aggregates included in the road pavement; if the road pavement consists of an asphalt mixture also bitumen vapours are produced due to the high temperature caused by the friction of the cutting tools.
In an open-air milling machine dust and vapours escape from the drum housing and from the conveyor belts, being emitted into the surrounding environment generating pollution and particularly close to the driving platform with potential health risk for the operator.
The main object of the present invention is to improve functionality of the road planer or milling machine in order to reduce pollution and other inconveniencies.
Patent EP 0 971 075 A1 foresees to fit a suction hood over the collecting conveyor and to connect said hood with a cyclone followed by a suction ventilator: said cyclone being located in the rear part of the milling machine.
This solution presents the following evident disadvantages:                the cyclone can knock down only the coarse dust particles, but it is not efficient at all in retaining the fine dust which is spread around in the atmosphere close to the operator's platform and sometimes close to the engine cooling air intake. The coarse dust is discharged onto the ground thus increasing the amount of material to be removed to clean the milled surface.        the poor efficiency of the cyclone causes the ventilator to suck still dust-laden air which compromises the functionality of the unit in a short time.        
Patent DE 102 23 819 A1 foresees the suction of the polluted air from the channel on the collecting conveyor and to convey it into the channel on the loading conveyor by means of the same suction-ventilator. This solution consents to exhaust the air, polluted by dust and vapours, into the atmosphere far away from the operator's platform. However the solution suffers the following disadvantages:                the ventilator sucks dust-laden air which compromises the functionality of the unit in a short time.        no filtering system is foreseen able to agglomerate the dust and to limit its diffusion into the atmosphere.        
DE 10 2005 035 480 discloses a milling machine comprising a dust box arranged in front of a ventilator and assigned to a suction channel having an outlet for passing clean waste air directly into the atmosphere.
U.S. patent application Ser. No. 2005/0179309 discloses a milling machine with a suction device for the polluted air, whereby the milled material is enclosed by a channel, the suction device is connected to a rear channel section of the channel in the direction of the material transport and sucks off the air polluted during milling blowing off the cleaned air into the environment.
Patents EP 1 507 925 B1 and U.S. Pat. No. 7,219,964 B2 foresee to suck the polluted air from both the channel on the collecting conveyor and from the channel over the loading conveyor, where:                the collecting conveyor is equipped with a sealing device, consisting of sets of flexible flaps, located close to its discharge head, which oppose to the entry of external air but do not oppose to the flow of the milled material;        the channel on the collecting conveyor is connected to the corresponding channel on the loading conveyor by means of hoses with air intakes located upstream of the above mentioned sealing device;        sealing devices, consisting of sets of flexible flaps are provided for the loading conveyor such as for the collecting conveyor. On the loading        conveyor the sealing devices are located downstream of the connection points of the above hoses with the loading conveyor channel and downstream of the suction-filtering unit;        the discharge area of the collecting conveyor onto the loading conveyor is not involved in the suction of the polluted area;        the polluted air is forced to pass through a filtering unit before being exhausted by the suction-ventilator into the atmosphere.        
The disadvantages of the solution are the following:                the bulk hoses connecting the channels of the two conveyors and the movements of said hoses caused by the slewing of the loading conveyor, compromise functionality;        the discharge area of the collecting conveyor onto the loading conveyor is not interested by the suction process. In said area dust and vapours are emitted and spread into the atmosphere in the vicinity of the operator's platform.        